This proposal aims to study the cortical representation of the sensory aspect of pain and touch within the traditionally defined secondary somatosensory cortex (SII) located along the Sylvian fissure in non-human primates. By using high resolution fMRI and image-guided electrophysiological recordings in anesthetized squirrel monkeys, we will examine functional roles of the subregions within SII in the processing of basic features of painful and tactile inputs. There are two specific aims. Aim 1 proposes to determine which subregion(s) within SII cortex is activated during painful and tactile stimulation of individual fingerpads;whether nociceptive and tactile responses colocalize within each activated subregion;whether there is a fine digit topography and stimulus intensity-dependent response for pain and/or touch;and what is the temporal property of the responses. FMRI activation maps to painful heat and vibration will be compared to evaluate the specificity of activation. Aim 2 proposes to determine the neuronal mechanism underlying the activations revealed by fMRI. FMRI activation maps will be validated and spatially correlated with the maps determined by electrophysiology. By using the fMRI activation maps as a guide, we will place single or multiple electrodes in the activated regions to characterize and record neuronal response properties in response to painful heat, vibration, and rest conditions, and to determine what aspect of neuronal activities (single, multiple neuron, or local field potential) correlates best with the stimulus-response function of the fMRI signal. This study will provide direct evidence relating the existence of nociceptive specific regions within SII cortex and the linkage between neuronal activities and fMRI signal. Ultimately, knowledge gained will have profound impact on our understanding of the cellular mechanism of pain processing and perception. 30 PUBLIC HEALTH RELEVANCE This study centers on understanding which cortical areas encode the location (where), intensity (how strong), and modality of a painful stimulus. If we can understand how these areas are organized and activated during sensory processing, and how they are connected to form a processing network, we will be able to understand the flowchart of information processing in the brain. This knowledge would promote new therapeutic ideas, which will lead to more rational and reliable treatment for pain.